Some things I’ve learned over the years about planning:

• If you are new at something, your time estimates will be way too low. Don’t be surprised if you need at least twice as much time. So initially, don’t plan more than half your day.
• Even when you gain experience after having done some things several times, there will always be a natural variation in the length of time they take.
• Don’t fill more than 70% of your day with planned items. You need time to deal with the unexpected. And it feels good to get things done in time, but it can be stressfull to get behind. By not overplanning you can organize success for yourself every day.
• Circumstances change, and so should your planning. Expect to change it frequently. Realize that this takes time, and budget for it.
• Evaluate your planning and actual progress at the beginning of the week, so you have a clear mental picture of what to do the coming week.
• The further you go into the future, the more fluid and empty your planning should be. Otherwise flexibility is impossible, and you’d be looking at a mountain of stuff to do, which can be disheartening.
• Don’t chop your day up into pieces smaller than 15 minutes. Again the mountain of stuff to do thing.